Introduction to Surfactant Self‐Assembly

Abstract

Current models and concepts are introduced and used to characterize the physical properties of homogeneous, small molecule, surfactant solutions such as the critical micelle concentration (cmc), aggregation number, degree of ionization of ionic aggregates and the interactions that determine the size and shape of aggregates, various mesophases such as spherical and rodlike micelles, lamellar, vesicular, bicontinuous, and reverse micelles, and the chemical reactivity in surfactant solutions. Surfactant aggregation is a spontaneous process and a delicate balance of forces governs the size and shapes of the structures at equilibrium. Aggregation is driven by the hydrophobic effect, the minimization of surfactant tail‐water contact by transfer of the tail of the surfactant unimer from water to the aggregate core with the concomitant release of water of hydration, and an increase in the entropy of the system. Balance is provided by a combination of electrostatic, ion‐specific, and hydration interactions in the interfacial region of the aggregates. Two models are generally used to interpret surfactant aggregation and solution properties, the more generally applied pseudophase model and the mass action model. For example, pseudophase models provide a comprehensive interpretation of micellar effects on chemical reactivity. A major unsolved problem is developing a general interpretation of ion‐specific effects, as exemplified by the Hofmeister series on surfactant aggregate properties. The ion‐pair hydration model represents one potential solution.

Influence of AO chain length, droplet size and oil to water ratio on the distribution and on the activity of gallates in fish oil-in-water emulsified systems: Emulsion and nanoemulsion comparison

“…Surfactants and oil molecules exchange very fast. The exchange of surfactants between micelles and the aqueous solution taking place in around 10 −6 s, and the mean lifetime of a micelle is around 10 −3 s (Romsted, 2012). Thus, both micelles and nanoemulsion drops can acquire excess of surfactant by adsorption of the surfactant at the oil-water interface from micelles that coalesce or dissociate nearby the droplets, allowing surfactant molecules to be adsorbed (Gruner et al, 2016;Malassagne-Bulgarelli & McGrath, 2009).…”

To Model Chemical Reactivity in Heterogeneous Emulsions, Think Homogeneous Microemulsions

“…Nevertheless, the high cooperativity driven by an increase in entropy of the system and multiple weak intermolecular interactions are sufficient to maintain the oil, interfacial, and water organization. 10,11 When the bulk composition is changed in a three-component system, both the number of intermolecular and ionic interactions and the number …”

Physical evidence that the variations in the efficiency of homologous series of antioxidants in emulsions are a result of differences in their distribution

“…7,12 -14 Our laboratory developed a methodology 7,12 -15 for determining the distributions of AOs in intact emulsions by exploiting the power of the pseudophase kinetic model, which was previously employed to model chemical reactions in surfactant-based systems (micelles, microemulsions, liposomes, etc.). 16 The method is based on the analyses of the surfactant effects with respect to the chemical reaction between the specially designed hydrophibic reactant (4-hexadecylbenzenediazonium (16-ArN 2 + ) tetrafluoroborate) and the AOs. With regard to the structural characteristics of 16-ArN 2 + , it is both oil insoluble (as a result of the cationic group) and water insoluble (as a result of hexadecyl hydrocarbon chain).…”